1. Field of the Invention
The present invention relates to a liquid discharge head having a switch circuit in a liquid discharge mechanism and a liquid discharge apparatus. Particularly, the present invention relates to an ink-jet recording head for forming an image by injecting energy into an ink discharge mechanism, discharging ink and attaching ink droplets on a recording medium and an ink-jet recorder. Moreover, the present invention relates to a liquid discharge head which can be applied to an apparatus used to fabricate a DNA chip, organic transistor or color filter and relates to a liquid discharge head for injecting energy into a liquid discharge element, discharging droplets and attaching the droplets on a medium.
2. Related Background Art
A recorder using an ink-jet recording system has been known so far as a liquid discharge apparatus. The recorder forms an image by heating ink, thereby generating bubbles to pressurize, and discharging the ink in accordance with the expansion motion of the bubbles and attaching discharged ink droplets on a recording medium. This recording system has advantages that it has a high recording quality and low noises. Moreover, the ink-jet recording system has advantages that color recording is comparatively easy, recording can be also applied to plain paper and an apparatus can be easily downsized. Furthermore, the ink-jet recording system can realize high-speed recording by arranging many discharge ports from which ink is discharged at a high density and is widely used for information output units such as a printer and facsimile.
The recording head of the ink-jet recording system generally has a discharge port for discharging ink, an ink route communicating with the discharge port and an electrothermal transducer for generating heat energy when voltage is applied. The electrothermal transducer is a thin-film heating resistor in general.
FIG. 9 is a sectional view showing a part of a conventional ink-jet recording head. A heating resistor 1033 is formed on a silicon substrate 1031. Moreover, an oxide film 1032 serving as a heat storing layer and an insulating layer is formed between the heating resistor layer 1033 and silicon substrate 1031. In the case of the heating resistor layer 1033, a region between connected electrode wirings 1034 functions as a heating resistor 1033a, which is heated when a pulsed voltage is applied to generate thermal energy and bubbles in ink in an ink route. When bubbles of the ink are generated, impacts are generated due to a chemical reaction of the ink or growth or disappearance of bubbles. To protect the heating resistor 1033a from these impacts, a tantalum (Ta) protection film 1036 is formed on the heating resistor layer 1033. An insulating protective layer 1035 made of silicon nitride (SiN) or the like is further formed under the Ta protection film 1036 in order to electrically insulate the heating resistor layer 1033 from the Ta protection film 1036.
According to the above configuration, the thermal energy generated from the heating resistor 1033a is transferred through the SiN insulating protection film 1035 and Ta protection film 1036 formed on the heating resistor 1033a in accordance with a heat conduction phenomenon. Thereby, heat is supplied to the ink on the Ta protection film 1036 and bubbles 1039 are generated in the ink. When the bubbles 1039 are generated, the ink around a nozzle 1037 serving as a discharge port of the ink is pressurized and ink droplets 1038 are discharged from the nozzle 1037.
To improve the quality of an image in recent years, the ink discharged from a discharge port tends to decrease in size. Therefore, the number of ink droplets necessary for forming the same image on one sheet is extremely increased. For example, to form an image of 15% density on a A4 sheet (210 mm×297 mm) at a density of 1,200×1,200 dots for 25.4 mm2 (one square inch), the number of dots of ink of the same color becomes 1.9×107 dots/sheet. To form a color image, inks of various colors are formed on a sheet at this number of dots. Moreover, in the case of an apparatus such as a printer to which an ink-jet recording head is applied, acceleration is progressed and improvement of the number of durable recording sheets is strongly requested. To improve the number of durable recording sheets, it is necessary that ink droplets are discharged from a discharge port for a long time in the same direction at the same quantity and same speed.
However, when discharge of ink is repeated, the ink may be scorched on the surface of the Ta protection film 1036 shown in FIG. 9 and when the ink is scorched, the stability for forming bubbles is deteriorated. Moreover, when discharge of ink is repeated, the Ta protection film 1036 is shaved and becomes thin and a phenomenon that ink penetrates the Ta protection film 1036 may occur. Thereafter, infiltration of ink progresses to the insulating protection film 1035 formed on the heating resistor 1033a, the ink infiltrates up to the heating resistor 1033a and the electrode wiring 1034 connected to the heating resistor 1033a, galvanic corrosion progresses in the electrode wiring 1034 and finally the electrode wiring 1034 may be disconnected.
FIGS. 10A and 10B are graphs showing changes in temperature of the heating resistor 1033a and changes in surface temperature of the Ta protection film 1036 of a conventional ink-jet recording head. FIG. 10A is a graph showing changes in temperature of the heating resistor 1033a to which the thermal energy is supplied and changes in surface temperature of the Ta protection film 1036. FIG. 10B is a graph showing the waveform of a pulse voltage applied to the heating resistor 1033a. In FIG. 10A, the temperature of the heating resistor 1033a is shown by a continuous line and the surface temperature of the Ta protection film 1036 is shown by a dotted line.
The temperature of the heating resistor 1033a and the surface temperature of the Ta protection film 1036 become T0 same as the room temperature at the time t0 when a pulse voltage is input to the heating resistor 1033a. When the pulse voltage is input to the heating resistor 1033a, the temperature of the heating resistor 1033a and the surface temperature of the Ta protection film 1036 which are T0 same as the room temperature rise. At the time t1 when the surface temperature of the Ta protection film 1036 reaches T1 (=approx. 300° C.), bubbles are generated on the interface between the Ta protection film 1036 and ink. In this case, the temperature of the heating resistor 1033a already reaches T2. Because bubbles are generated, heat is not propagated from the surface of the Ta protection film 1036 to the ink. Therefore, the surface temperature of the Ta protection film 1036 starts a sudden rise. Similarly, the temperature of the heating resistor 1033a also suddenly rises. These temperatures show the vertex at the time t3 when application of the pulse voltage to the heating resistor 1033a is stopped and values of the temperatures becomes TP1 and TP2 respectively. After the time t3 when application of the pulse voltage to the heating resistor 1033a is stopped, thermal energy is not generated from the heating resistor 1033a. Therefore, the temperature of the heating resistor 1033a and the surface temperature of the Ta protection film 1036 suddenly lower and return to the original room temperature T0. It is experimentally clarified that the durability of the ink-jet recording head is extremely improved by decreasing the interval between the time t3 when application of the pulse voltage input to the heating resistor 1033a is stopped and the time t1 when bubbles are generated and lowering the highest reaching temperature TP1 of the heating resistor 1033a and the highest reaching temperature TP2 of the Ta protection film 1036.
To lower the highest reaching temperature TP1 of the heating resistor 1033a and the highest reaching temperature TP2 of the Ta protection film 1036, various devices are made. It is an example to set a temperature sensor to an ink-jet recorder, sense the temperature of in ink-jet recording head by the temperature sensor and set a controller for modulating the width of a pulse voltage for driving a heating resistor to the printer body. However, the temperature sensor is used to measure the temperature of the whole ink-jet recording head but it is not used to accurately measure the temperature near the heating resistor. Moreover, Japanese Patent Application Laid-Open No. 2001-341355 (Patent Document 1) discloses an example of setting a controller for controlling the time for driving a plurality of heating resistors to the body of a printer when the heating resistors are simultaneously driven and the number of heating resistors to be driven is sequentially changed in accordance with the number of heating resistors to be simultaneously driven.
As means for solving the problem of the above conventional ink-jet recording head, there is the configuration disclosed in Japanese Patent Application Laid-Open No. 2001-129995 (Patent Document 2). FIG. 11 shows a configuration in which a semiconductor diffusion resistor 1040 formed by diffusing impurities immediately below the heating resistor 1033a having the structure shown by a sectional view of a conventional ink-jet recording head (FIG. 4) is arranged. Moreover, FIG. 12 shows a circuit block diagram of an ink-jet recording head using the structure in FIG. 11.
FIG. 12 is an equivalent circuit diagram of the control portion of the ink-jet recording head shown in FIG. 11. The equivalent circuit of the control portion of the ink-jet recording head is constituted of the heating resistor 1033a, a power supply 1011 for supplying power to the heating resistor 1033a, a switch 1013 to be turned on when a switch driving signal 1017 is input, a sensor 1014 for outputting a control signal 1016 when detecting occurrence of bubbles and a driving control circuit 1018 for inputting an image input signal 1015 and the control signal 1016 and outputting a switch driving signal 1017. The sensor 1014 detects occurrence of bubbles by using a change of resistance values of the semiconductor diffusion resistor 1040. It is possible to accurately estimate a temperature difference from the surface temperature of the Ta protection film 1036 in accordance with thicknesses, thermal conductivities or densities of the insulating protection film 1035 and Ta protection film 1036. Therefore, the sensor 1014 can detect occurrence of bubbles by determining the surface temperature of the Ta protection film 1036 from the electric resistance value of the semiconductor diffusion resistor 1040.
When the image input signal 1015 is not input, the driving control portion 1018 does not output the switch driving signal 1017 and the switch 1013 is kept turned-off. When the image input signal 1015 is input to the driving control portion 1018 but the control signal 1016 is not input to it, the driving control portion 1018 outputs the switch driving signal 1017. Then, the switch 1013 is turned on and the heating resistor 1033a produces heat. However, even if the image input signal 1015 is input to the driving control portion 1018, when occurrence of bubbles is detected by the sensor 1014 and the control signal 1016 is input to the driving control portion 1018, the driving control portion 1018 does not output the switch driving signal 1017 but the switch 1013 is turned off.
According to the above configuration, it is detected that bubbles on ink are generated from a change of resistance values of the semiconductor diffusion resistor 1040 caused by heat generation of the heating resistor 1033a. Moreover, it is proposed to stop voltage application to the heating resistor in accordance with the detection result, restrain extra heat generation of the heating resistor 1033a and improve the durability of an ink-jet recording head.
Moreover, Japanese Patent Application Laid-Open No. H07-068907 discloses a configuration provided with detection means for detecting a voltage applied to a piezoelectric element and blocking means for blocking switching means in accordance with a detection result by the detection means in order to prevent an ink-jet recording head for detecting a short circuit of a piezoelectric element to control a power supply switch from being damaged due to a short circuit.
However, the conventional ink-jet recording head shown in FIG. 9 detects the general temperature of the ink-jet recording head as a representative value but it does not detect the temperature of each heating resistor.
Therefore, the pulse width of a pulse voltage to be applied to a heating resistor for actual driving is not set for every individual heating resistor by considering the fluctuation of the total resistance value of a heating resistor, power-supply wiring resistance and switch circuit but it is set to the maximum pulse width necessary for ink to be expanded and discharged in a certain ink-jet recording head. In other words, a pulse voltage more than necessity is applied to a certain heating resistor to cause the durability and stability of a recording head to deteriorate. Therefore, combination of power-supply wiring resistances is used as one of correction means for decreasing the fluctuation of the total resistance value of a heating resistor, power-supply wiring resistance and switch circuit in an ink-jet recording head. Detection and setting of the maximum pulse width necessary for ink to be expanded and discharged is performed when the ink is shipped from a factory and its result is recorded in and set to a nonvolatile memory (EEROM) set in a recording head. Therefore, only by preparing the comparatively expensive nonvolatile memory, the cost of the printer body increases.
Moreover, in the case of the configuration (refer to FIGS. 11 and 12) disclosed in Patent Document 2, the heat generated by each heating resistor is detected, its detection result is fed back to a driving control portion and a pulse width is controlled for each heating resistor. Therefore, unnecessary voltage application time disappears and it is possible to improve the durability of a heating resistor and the durability of a recording head in its turn. However, because it is necessary to embed a semiconductor diffusion resistor immediately under a heating resistor, the configuration of a heating resistor region becomes complex and a physical step more than necessity is formed around a heating resistor. Therefore, the configuration and function of a nozzle portion may be greatly affected.
The present invention is made to solve the above problems and its object is to provide a liquid discharge head capable of improving the durability and stability of a liquid discharge mechanism (heating resistor) and a liquid discharge head in its turn without making the shape of the region of the liquid discharge mechanism complex.